(1) Field of the Invention
This invention relates to a clamping device having two blow molds each comprising a split mold in a back-to-back relation, said blow molds capable of being clamped simultaneously by clamping cylinders respectively externally and internally provided.
(2) Prior Art
A clamping device capable of simultaneously clamping two blow molds arranged in a back-to-back relation is described in Japanese Patent Laid-Open Nos. 59-67020 and 60-96436. These known clamping devices have a construction in which opening and closing of a mold is also carried out by a clamping cylinder, which inevitably requires a rod for alternately connecting split molds or a rod for alternately connecting a split mold and a clamping plate.
The above-described conventional devices have are suffered from problems in that since the opening and closing of a mold is carried out by the clamping cylinder, the opening and closing speed is slow; in the former, a blow mold and a clamping ram are connected to a mold mounting plate provided in the central portion and the inside of the mold is received by a spacer, and therefore, as the number of cavities increases to lengthen the blow mold, both sides of the blow mold tend to be flexed due to the internal pressure; and in the blow mold, parting lines remarkably appear on the sides of a molded article to impair the product value of the molded article.
The latter has a construction in which a blow mold is mounted on a clamping plate inserted through tie bars provided on a fixed plate, and the blow mold is clamped with the clamping plate. Therefore, a flexure due to the internal pressure is hard to occur but a number of clamping plates are required, and as a result an opening and closing space becomes necessary, and therefore, the clamping device becomes large as compared with the former, posing a new problem in that mounting of the clamping device on a molding machine is subjected to limitation.